This invention relates to an interface for use in a combined liquid chromatography -- mass spectrometry system.
A chromatograph is means effective for separating and analyzing a sample, while a mass spectrometer is means effective for obtaining information on the molecular weight and molecular structure of the sample. There has been developed a system in which the chromatograph and the mass spectrometer are coupled and which performs the analyses of a sample continuously from the quantitative analysis to the qualitative analysis. Among such systems, one employing a liquid chromatograph as the chromatograph has the feature of being effective for the continuous analyses of, particularly, a substance which is difficult to be separated and analyzed by the gas chromatography, for example, a substance which is thermally unstable or a substance whose volatility is low. In such combined liquid chromatography -- mass spectrometery system, it is necessary to selectively take only the sample out of an effluent from the liquid chromatograph and to supply it to the mass spectrometer. The effluent from the liquid chromatograph contains the sample and a solvent in large quantities relative to the sample, and the solvent must be separated and removed from the effluent. Further, in order to obtain a more accurate mass spectrum of the sample, an enriched sample need be introduced into the mass spectrometer. To this end, an interface is usually provided between the liquid chromatograph and the mass spectrometer. Thus, the two requirements are fulfilled.
As to such interface, there has been known, for example, W. H. McFadden and H. L. Schwartz, "Direct Analysis of Liquid Chromatographic Effluents," Journal of Chromatography, 122 (1976) 389-396, in which a ribbon transport LC - MS interface is disclosed. In this interface, an annular ribbon made of stainless steel circulates through two vacuum locks and a heater which are interposed between the liquid chromatograph and the mass spectrometer. The effluent from the liquid chromatograph is placed on the stainless-steel ribbon. A part of the solvent is removed by heating etc., whereupon the remaining solvent is removed in the two vacuum locks. Lastly, the sample left behind is heated and vaporized by the heater. The vaporized sample is guided to an ion source of the mass spectrometer. Partition plates forming the vacuum locks are provided with slots of very small diameter for passage of the stainless-steel ribbon.
Such interface, however, has the following disadvantages. A preceding sample adhering to the surface of the slot mixes into a succeeding sample, and becomes the cause for the memory effect of the sample spectrum. It is possible that the quality of a sample will be changed by the stainless steel. Further, the change of the quality of the sample is brought about by heating the sample for the vaporization at a high temperature. At a higher solvent flow-rate, sample is lost due to spray evaporation at the first vacuum lock.